1. Field of the Invention
This invention relates to a seatbelt retractor to be mounted in a backrest. More specifically, this invention is concerned with a seatbelt retractor in which the spatial orientation of a sensing member responsible to a sudden acceleration, collision or deceleration is suitably adjustable depending on the angle of reclining of the backrest.
2. Description of the Related Art
As retractors for seatbelt systems each of which is used to safely hold a vehicle occupant or the like in a seat, emergency locking retractors have been used conventionally. To assure effective and safe restraint of an occupant, an emergency locking retractor is provided with an emergency locking mechanism to physically lock it by a sensing member which responds to a sudden acceleration, collision or deceleration.
Sensing members employed in these emergency locking retractors include those capable of sensing accelerations or tiltings of vehicle bodies. Such sensing members are each constructed in such a way that, when an inertia member is caused to move as a result of a collision of a vehicle body, for example, a sensor arm arranged on an upper part of the inertia member is caused to swing and a locking mechanism for locking rotation of a takeup spindle, on which a webbing is wound, in a webbing-releasing direction is then actuated.
In recent years, proposals have been made about seatbelt systems of the type that a retractor such as that mentioned above is mounted in a backrest of a reclining seat for a vehicle or the like and is operable similarly even when an angle of reclining of the backrest is changed.
For example, a seatbelt system disclosed in German Utility Model No. 8503541 makes it possible to maintain the spatial orientation of a sensing member in a suitable orientation irrespective of the angle of reclining of a backrest by causing a wire to move in accordance with a reclining operation of the backrest such that a sensor case is caused to pivot by the wire.
The above-described sensor case of the seatbelt system, however, undergoes swinging about a shaft which is located adjacent a position where a sensor arm and a ratchet wheel engage, so that the manner of contact (angle of contact) between a free end of the sensor arm and the ratchet wheel changes when the backrest is reclined and the spatial orientation of the sensing member varies. This change in the manner of contact involves a potential problem in that the sensor arm may fail to stop the ratchet wheel at a predetermined position and hence to allow a locking mechanism to function properly.
In a retractor making use of ratchet wheel, there is a correlation between the position of a sensor arm of a sensing member and a position where a locking mechanism is actuated, and a predetermined phase has been set. Moreover, there is a limitation to the position of the sensing member, where the locking mechanism can be properly actuated, and accordingly, it is improper to arrange the sensing member at a position other than the above-mentioned position. In a locking mechanism of the type that a rotation preventing member arranged on a takeup spindle is brought into engagement with an engaged tooth arranged on a retractor base when a ratchet wheel arranged on the takeup spindle is stopped from rotation and relative rotation takes place between the ratchet wheel and the takeup spindle, the timing of actuation of the locking mechanism varies unless the engaged tooth of the retractor base, said engaged tooth serving to set a locking position, and the engaged teeth of the ratchet wheel is constant in phase. In a construction of the type that locking is achieved by an engagement of a rotation preventing member with one of engaged teeth continuously arranged on a retractor base, a variation in the timing of actuation of the rotation preventing member may lead to such a situation that the rotation preventing member fails to reach a position where the rotation preventing member is supposed to engage one of the engaged teeth, thereby resulting in an insufficient engagement. Forced rotation of the takeup spindle to make this engagement sufficient is however not preferred because unduly large force acts, for example, on a sensor arm or the like. If the timing of actuation of the rotation preventing member varies and the position of the rotation preventing member and that of the engaged teeth of the retractor base become too close to each other, on the other hand, the rotation preventing member and the engaged teeth of the retractor base may hit each other at their edges, thereby possibly resulting in damages to the engaged teeth.